Oxidative phosphorylation enzymes in normal and neoplastic cell growth

Cancer cells, despite growing aerobically, have the propension to utilize the glycolytic pathway as energy source. This biochemical phenotype is accompanied by a decreased content of mitochondria and, paradoxically, by enhanced transcription of nuclear and mitochondrial-encoded genes for the enzymes of oxidative phosphorylation (OXPHOS). The role of OXPHOS enzymes in normal and neoplastic cell growth has been studied in liver regeneration and human hepatocellular carcinoma. In early liver regeneration characterized by active mtDNA replication, a decrease in the content and activity of ATP synthase occurs while transcription of the ATPsyn beta nuclear gene is activated. Translation of ATP synthase subunits seems, on the contrary, to be less effective in this phase. In the second replicative phase of liver regeneration, the repression of ATPsyn beta translation is relieved and normal cell growth starts. In this replicative phase the recovery of the liver mass appears to be directly related to the recovery of the OXPHOS capacity. Mitochondria isolated from biopsies of human hepatocellular carcinoma exhibit a decreased rate of respiratory ATP synthesis (OXPHOS) and a decreased ATPase activity. The decline in the activity of the ATP synthase is found to be associated with a decreased content of the ATPsyn beta in the inner mitochondrial membrane. In neoplastic tissue the ATPase inhibitor protein (IF1) is overexpressed. This could contribute to prevent hydrolysis of glycolytic ATP in cancer cells. A peptide segment of IF1 (IF1-(42-58)-peptide), constructed by chemical synthesis, proved to be equally effective as IF1 in inhibiting the ATPase activity of the ATP synthase complex in the mitochondrial membrane deprived of IF1. The synthetic peptide might turn out to be a useful tool to develop immunological approaches for the control of neoplastic growth.

The onset of CML in blastic crisis: molecular features

The lack of distinguishing characteristics between lymphoid blastic crisis (BC) of Philadelphia (Ph)+ chronic myeloid leukemia (CML) and Ph+ acute lymphoblastic leukemia (ALL) remains an exciting dilemma. Indeed, the genetic defect of approximately half of Ph+ ALL patients is identical to that identified in CML. Here we report the case of one patient admitted with immunological and molecular patterns indicative of Ph+ ALL. The patient was brought into complete remission by chemotherapy and was transplanted with an HLA identical sibling donor, but relapsed a few months later with immunological and molecular evidence of BC of CML, displaying myeloid markers and lacking lymphoid antigens and immunoglobulin heavy chain (IgH) rearrangement. This suggest a CML case with an initial BC without a previous chronic phase or supervening on a subclinical CML.

Ursodeoxycholate promotes protein phosphorylation in the cytosol of rat hepatocytes

A study is presented of the effect of the bile salt ursodeoxycholate (UDC) on protein phosphorylation by [gamma-32P]ATP in the cytosol from rat hepatocytes. Gel electrophoresis and corresponding autoradiograms of cytosolic proteins show that UDC promotes phosphorylation of at least eight different protein bands. Four of them (the 36, 60, 64 and 76 kDa) are phosphorylated by Ca2+ and phospholipid-dependent protein kinase (PKC); three (the 31, 51 and 71 kDa) are phosphorylated by cAMP-dependent protein kinase (PKA) and one protein band, with molecular weight of 34 kDa, apparently contains substrates of both PKC and PKA. Data are reported indicating that UDC can directly affect the intrinsic activity of protein kinases.

Steady-state proton translocation in bovine heart mitochondrial bc1 complex reconstituted into liposomes

The effect of different anions on the steady-state proton translocation in bovine bc1 complex reconstituted in liposomes was studied. The H+/e- ratio for vectorial proton translocation is at the steady state definitely lower than that measured at level flow, (0.3 vs. 1.0). The presence of azide or arachidonate at micro- and submicromolar concentrations, respectively, gave a substantial reactivation of the proton pumping activity at the steady state, without any appreciable effect on respiration-dependent transmembrane pH difference. Addition of azide to turning-over bc1 vesicles also caused a transition of b cytochromes toward oxidation. The results are discussed in terms of possible involvement of an acidic residue in the protonation of the semiquinone/quinol couple at the N side of the membrane.

A possible role of slips in cytochrome C oxidase in the antioxygen defense system of the cell

Evidence is available showing that the coupling efficiency of the proton pump in cytochrome c oxidase of mitochondria can under certain conditions decrease significantly below the maximum attainable value. The view is developed that slips in the proton pump of cytochrome c oxidase represent an intrinsic switch mechanism which regulates the relative contribution of energy transfer and respiratory protection against oxygen toxicity by the oxidase.

Redox-linked protolytic reactions in soluble cytochrome-c oxidase from beef-heart mitochondria: redox Bohr effects

A study is presented of co-operative redox-linked protolytic reactions (redox Bohr effects) in soluble cytochrome-c oxidase purified from bovine-heart mitochondria. Bohr effects were analyzed by direct measurement, with accurate spectrophotometric and potentiometric methods, of H+ uptake and release by the oxidase associated with reduction and oxidation of hemes a and a3. CuA and CuB in the unliganded and in the CN- or CO-liganded enzyme. The results show that there are in the bovine oxidase four protolytic groups undergoing reversible pK shifts upon oxido-reduction of the electron transfer metals. Two groups with pKox and pKred values around 7 and > 12 respectively appear to be linked to redox transitions of heme a3. One group with pKox and pKred around 6 and 7 is apparently linked to CuB, a fourth one with pKox and pKred of 6 and 9 appears to be linked to heme a. The possible nature of the amino acids involved in the redox Bohr effects and their role in H+ translocation is discussed.

Gene BR140, which is related to AF10 and AF17, maps to chromosome band 3p25

The genes AF10 and AF17 have been identified as the basis of the t(10;11) and t(11;17) translocations, events that result in their fusion to the MLL/HRX gene in acute myeloid leukaemias. AF10 and AF17 bear significant homology to each other within their putative zinc finger and leucine zipper domains, although they are diverged outside these regions. The BR140 gene encodes a 140 kDa protein of unknown function that contains a putative zinc finger domain, a leucine zipper region, and, in addition, a bromo domain. The zinc finger and leucine zipper domains of BR140 have significant homology to those of AF10 and AF17, suggesting that it belongs to this newly described gene family and, therefore, could be a target for chromosome translocation. To assess the potential involvement of BR140 in chromosome translocations in leukaemia, the chromosomal location of the BR140 gene has been determined by using several independent methods. A combination of Southern analysis, polymerase chain reactions (PCR) on monochromosomal cell hybrids, and fluorescence in situ hybridisation (FISH) has been used to show that the BR140 gene maps to chromosome band 3p25.

The effect of mild trypsin digestion of F1 on energy coupling in the mitochondrial ATP synthase

Mild trypsin digestion of isolated bovine-heart mitochondrial F1-ATPase removed the first 15 residues from the N-terminus of subunit alpha under conditions in which other F1 subunits were apparently untouched. When the trypsinized F1 (TF1) was reconstituted with the F0 sector in the mitochondrial membrane (USMP), the ATP hydrolase activity acquired oligomycin sensitivity but ATP hydrolysis was decoupled from proton pumping. TF1 added to USMP did not block the proton channel in F0 as the native F1 did. AMP-PNP inhibited proton conductivity in reconstituted F1-USMP but this effect was lost in reconstituted TF1-USMP. These results indicate that the N-terminus of the F1 alpha subunit plays a critical role in the conformational communication between F1 and F0.

Topology of the mitochondrial cAMP-dependent protein kinase and its substrates

In intact bovine heart mitochondria, cAMP-dependent phosphorylation of 42, 29, 18 and 6.5 kDa proteins was inhibited by carboxyatractyloside. This shows that both mitochondrial cAMP-dependent protein kinase (mtPKA) and its protein substrates are localized at the matrix side of the inner mitochondrial membrane. Proteins of 42, 29, 18, and 6.5 kDa were also bound at the outer surface of mitochondria where they were phosphorylated by the added purified catalytic subunit of PKA. In the cytosol from bovine heart proteins of the above molecular weights were phosphorylated by the cytosolic PKA.

MK-801 prevents levodopa-induced motor response alterations in parkinsonian rats

The systemic administration of the N-methyl-D-aspartate (NMDA) receptor antagonist, MK801 ((+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine) , has previously been found to reverse the motor response alterations that develop during long-term levodopa treatment of parkinsonian rats. To determine whether co-administration of MK801 with levodopa might prevent the initial appearance of these response changes, rats, rendered parkinsonian by a 6-hydroxydopamine lesion of the medial forebrain bundle, received either levodopa alone or levodopa with the NMDA receptor antagonist. After four weeks of treatment with levodopa alone, the duration of the turning response declined by 37% (P < 0.05) and the number of ineffectual levodopa injections had more than doubled (P < 0.05). MK801 co-treatment completely blocked the shortening in response duration and prevented the frequency of ineffectual levodopa injection from exceeding baseline levels in animals receiving levodopa alone. The total magnitude of the turning response to levodopa was not affected. These results suggest that NMDA receptor blockade may act prophylactically to prevent the appearance of motor response alterations in levodopa-treated parkinsonian rodents that resemble those occurring in levodopa-treated patients with Parkinson's disease.

Identification of functional domains and critical residues in the adenosinetriphosphatase inhibitor protein of mitochondrial F0F1 ATP synthase

Peptide segments of the inhibitor protein (IF1) of the F0F1 ATP synthase complex from bovine-heart mitochondria have been constructed by chemical synthesis. The IF1-(42-58)-peptide was equally effective as IF1 in inhibiting the ATPase activity of both the F0F1 complex in the mitochondrial membrane deprived of IF1 (SMP) and soluble F1. The IF1-(22-46)-peptide inhibited the ATPase activity in the soluble F1 but had no effect on either the ATPase activity or H+ conduction in SMP. Substitution of the His or Lys residues with Ala in the IF1-(42-58)-peptide decreased the inhibition of ATP hydrolysis. The inhibition exerted by the IF1-(42-58)-peptide on ATP hydrolysis in SMP exhibited a pH dependence, similar to that observed with IF1, which was lost upon replacement of His or Lys with Ala. In soluble F1, inhibition of ATP hydrolysis by IF1, the IF1-(42-58)-peptide and the IF1-(22-46)-peptide was pH dependent when F1 was first incubated with ATP. The IF1-(42-58)-peptide also caused inhibition of passive H+ conduction in SMP. This activity of the synthetic peptide was weaker, as compared to that of IF1, and practically unaffected by substitution of His or Lys with Ala. An antibody against the IF1-(42-58)-synthetic peptide stimulated ATP hydrolysis in the membrane-bound F0F1 complex with associated IF1 but was without effect on H+ conduction. An antibody against IF1 stimulated both processes.

Factors affecting the H+/e- stoichiometry in mitochondrial cytochrome c oxidase: influence of the rate of electron flow and transmembrane delta pH

A study is presented of the factors affecting the H+/e- stoichiometry of the proton pump of mitochondrial cytochrome c oxidase, isolated and reconstituted in phospholipid vesicles (COV). Under level flow conditions, i.e., in the absence of a transmembrane delta muH+, the H+/e- ratio, obtained from spectrophotometric measurements of the initial rates of electron flow and H+ release specifically elicited by cytochrome c, varied from around 0 to 1, depending on the actual rate of electron flow through the oxidase. At steady state the H+/e- ratio for the oxidase was specifically depressed by the transmembrane delta pH. The study of the H+/e- ratio of the pump was complemented by an analysis of the redox pattern of cytochrome c, CuA, and heme a. From both sets of results and recent structural data from other groups, it is concluded that the dependence of the H+/e- ratio on the rate of electron flow through the oxidase and transmembrane delta pH is associated with the possible occurrence of two electron transfer pathways in cytochrome c oxidase, a coupled one (cyt c-->CuA-->heme a-->heme a3-CuB) and a decoupled one (cyt c-->CuA-->heme a3-CuB). The contributions of the two pathways, differently affected by kinetics and thermodynamic factors, will determine the actual H+/e- ratio of the pump. A possible role of heme a in the proton pump and the physiological implication of the variable H+/e- ratio in the oxidase are discussed.

Synthesis and biological activity of a series of isoindolone derivatives related to cytochalasins

A series of hydrogenated isoindolone derivatives structurally related to cytochalasin B has been synthesized and their ability to induce binucleation in the human lymphocytes were tested. All compounds were found able to inhibit cell cytokinesis at different extent in the range (3.12-25 mumol/l) respect to the negative control; however the highest percentage of binucleated cells is induced by Cyt B.

Oxidative phosphorylation and F(O)F(1) ATP synthase activity of human hepatocellular carcinoma

A study of mitochondrial oxidative phosphorylation in biopsies from human hepatocellular carcinoma is presented. Tumour mitochondria as compared to control liver mitochondria, besides a reduced activity of complex IV (cytochrome c oxidase) of the respiratory chain, show a decreased phosphorylative capacity. This appears to be mainly related to a defective F o F(1) ATP synthase complex. Use of an antibody against the F(1) portion of the complex demonstrate a definite decrease for the beta subunit of F(1) in tumour mitochondria.

The Saccharomyces cerevisiae OXA1 gene is required for the correct assembly of cytochrome c oxidase and oligomycin-sensitive ATP synthase

The nuclear gene OXA1 was first isolated in Saccharomyces cerevisiae and found to be required at a post-translational step in cytochrome c oxidase biogenesis, probably at the level of assembly. Mutations in OXA1 lead to a complete respiratory deficiency. The protein Oxa1p is conserved through evolution and a human homolog has been isolated by functional complementation of a yeast oxa1- mutant. In order to further our understanding of the role of Oxa1p, we have constructed two yeast strains in which the OXA1 open reading frame was almost totally deleted. Cytochrome spectra and enzymatic activity measurements show the absence of heme aa3 and of a cytochrome c oxido-reductase activity and dramatic decrease of the oligomycin sensitive ATPase activity. Analysis of the respiratory complexes in non-denaturing gels reveals that Oxa1p is necessary for the correct assembly of the cytochrome c oxidase and the ATP synthase complex.

The nuclear-encoded 18 kDa (IP) AQDQ subunit of bovine heart complex I is phosphorylated by the mitochondrial cAMP-dependent protein kinase

In bovine heart mitochondria a protein of M(r) 18 kDa, phosphorylated by mtPKA, is associated to the NADH-ubiquinone oxidoreductase in the inner membrane and is present in purified preparation of this complex. The 18 kDa phosphoprotein has now been isolated and sequenced. It is identified as the 18 kDa (IP) AQDQ subunit of complex I, a protein of 133 amino acids with a phosphorylation consensus site RVS at position 129-131.

Ageing is associated in females with a decline in the content and activity on the b-c1 complex in skeletal muscle mitochondria

The activity of cytochrome-c oxidase [E.C. 1.9.3.1] and b-c1 complex [E.C. 1.10.2.2] and the content of cytochromes b, c + c1 and a + a3 in human skeletal muscle mitochondria from orthopaedic patients (108 women and 68 males), of age ranging between 10 and 50 years, have been analyzed. The activity of cytochrome c-oxidase declines with age both in females and males. The activity of b-c1 complex, which in young females is significantly higher than in young males, declines sharply in females, but not in males, with ageing. These results reveal that the content of active b-c1 complex in muscle mitochondria is specifically controlled by female sex hormones.

Characterization of proteins phosphorylated by the cAMP-dependent protein kinase of bovine heart mitochondria

Characterization of two mitochondrial proteins of M(r) 42 and 18 kDa, respectively, phosphorylated by the cAMP-dependent protein kinase of bovine heart mitochondria (mtPKA), is presented. A 42 kDa protein is found to be loosely associated to complexes I, III and IV of the respiratory chain and complex V (ATP synthase) in the inner mitochondrial membrane. An 18 kDa protein is associated to complex I in the inner membrane and in a purified preparation of this complex where it can be phosphorylated by the isolated catalytic subunit of PKA.

Functional analysis of subunits III and IV of Bacillus subtilis aa3-600 quinol oxidase by in vitro mutagenesis and gene replacement

Using the high efficiency of homologous gene recombination in Bacillus subtilis, a strategy for mutational analysis of the proton pumping aa3-600 quinol oxidase of this organism has been developed. The qox operon with the qoxA, qoxB, qoxC and qoxD genes, coding for the four subunits of this oxidase, was deleted and then replaced with mutated copies in which qoxC (subunit III) or qoxD (subunit IV) genes were deleted. The complete deletion of the qox operon caused disappearance of heme aa3-600 and a slight depression of the overall respiratory activity, compensated by alternative oxidase with no proton pumping activity. Deletion of qoxC probably resulted in a defective assembly of the aa3-600 quinol oxidase. The strain with deletion of qoxD gene expressed normal content of heme aa3-600 but exhibited a reduced respiratory activity and a significantly depressed proton pumping activity. These results show that subunit IV is critical for the activity of the proton pumping aa3-600 quinol oxidase.

Correlation between rat liver regeneration and mitochondrial energy metabolism

The time course of changes in mitochondrial energy metabolism during liver regeneration, following partial hepatectomy, is analyzed. For 24 h after surgical operation, a lag phase in the time course of the growth of liver is observed. In this period mitochondria showed a decrease of: (1) the respiratory control index; (2) the rate of oxidative phosphorylation; (3) the amount of immunodetected beta-F1 and F01-PVP subunits of F0F1-ATP synthase. No decrease, but instead a small increase in the content of mRNA for beta-F1 was observed in this phase. After this lag phase the growth of liver started, the content of mRNA for beta F1, as well as the level of immunodetected mitochondrial beta-F1 and F01-PVP subunits, increased and oxidative phosphorylation recovered. Analysis of the relative beta F1 protein/mRNA ratio indicates a decrease of beta F1 translational efficiency which remained low up to 72 h after partial hepatectomy and reached the same ratio of control at 96 h. It is concluded that the regenerating capability of rat liver is correlated with the efficiency of oxidative phosphorylation.

[The role of the radiological hemithorax examination in closed trauma of the chest]

January, 1992, to September, 1994, a hundred and seventy-eight blunt chest trauma patients were examined with plain chest films and detailed rib studies. The patients were subdivided into three groups according to: a) the presence/absence of rib fractures correlated with clinical data; b) the depiction of rib fractures and/or thoracic complications; c) treatment customization in the presence/absence of rib fractures. In our series of patients the clinical data and the presence of rib fractures were poorly correlated. The detection rates of minor and major complications were also investigated on plain chest films and detailed rib studies. Plain chest films most frequently depicted the complications requiring conservative or surgical management and gave the indication for further imaging investigations. The detailed rib studies of the involved hemithorax yielded no further information useful to therapy except in few cases: and should therefore be limited to the cases exhibiting complications on chest films, which may benefit from surgical fixation. The accurate study of rib fractures is paramount in the cases where legal action may be undertaken.